The terms “green diesel” and “renewable diesel” broadly refer to diesel-quality, non-FAME (fatty acid methyl ester) fuels derived from renewable resources (e.g., plant and/or animal sources) that are suitable for direct use in most ordinary compression ignition diesel engines. Renewable diesel is chemically distinguishable from biodiesel, which is primarily composed of fatty-acid-derived mono alkyl esters. The oxygen content of biodiesel is too high to be suitable as a direct replacement for conventional petroleum diesel. In contrast, renewable diesel is substantially oxygen-free and is indistinguishable from petroleum diesel. Thus, renewable diesel can replace petroleum diesel and/or be used in blends with petroleum diesel. Renewable diesel also has higher energy content per volume compared to biodiesel. Renewable diesel may be used or blended in aircraft fuel where oxygen-containing fuels are not allowed.
Conventional processes for converting renewable oils or fats, such as vegetable oil or animal fat, to renewable diesel include catalytic or thermal decarboxylation (removal of carbon dioxide), catalytic decarbonylation (removal of carbon monoxide) and catalytic hydrocracking. The products are expected to be simple hydrocarbons or olefins. The feed for these processes can be a triglyceride or a free fatty acid.
Commercially available deoxygenation catalysts suffer from several disadvantages such as poor stability, low activity, undesirable side reactions, and/or a need to operate under high pressure conditions in the presence of hydrogen gas.